This document claims priority to Japanese Patent Application No. 2001-132597 filed in the Japanese Patent Office on Apr. 27, 2001, and Japanese Patent Application No. 2001-132594 filed in the Japanese Patent Office on Apr. 27, 2001. The entire contents of those applications are hereby incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical scanning device and an image forming apparatus such as a copying machine, a facsimile machine, a printer, etc., including the optical scanning device.
2. Discussion of the Background
Generally, an optical scanning device of a flatbed scanner type that scans an image of an original document immovably set on a contact glass includes first and second moving carriages that move in a sub-scanning direction at a speed ratio of two to one. The first moving carriage carries a light source that irradiates an image surface of an original document with light and a first mirror that reflects the light reflected from the image surface of the original document. The second moving carriage carries at least one of a second mirror and a third mirror that reflects the light reflected from the first mirror.
The above-described optical scanning device employs a wire driving system in which the first and second moving carriages are driven via driving wires wired at both sides of the first and second moving carriages, respectively.
Alternatively, the above-described optical scanning device may employ a belt driving system in which the first and second moving carriages are individually driven via timing belts. Specifically, stepped pulleys including large-diameter pulleys and small-diameter pulleys are respectively arranged at both sides of the first and second moving carriages. Each diameter of the small-diameter pulleys is one-half that of the large-diameter pulleys.
Two pairs of endless-belt-like long and short timing belts are respectively spanned around the stepped pulleys including the large-diameter pulleys and small-diameter pulleys at both sides of the first and second moving carriages, i.e., four timing belts are provided in total. The both sides of the first moving carriage are respectively fixed to portions of the two long timing belts, and the both sides of the second moving carriage are respectively fixed to portions of the two short timing belts. With the above-described construction, the first and second moving carriages are individually driven via the long and short timing belts, respectively.
The above-described wire driving system has disadvantages as follows:
(1) The wiring of driving wires is so complicated that assembly work may not be easily accomplished. Therefore, auto-assembly of an optical system of a scanning device may be difficult to perform.
(2) In order to prevent driving wires from being tangled, a predetermined tension is necessary to be applied to the driving wires. Because of complicated wiring of the driving wires, many pulleys are required to rotatably support the driving wires. For example, at least two pulleys are required at one side of the moving carriages. Due to the tension applied to the driving wires, the force in the radial direction is exerted on each of the pulleys. In this case, a ball bearing is often used for each of the pulleys to reduce a load on the pulley, driving the cost of the device higher.
Next, an example of a background optical scanning device employing the above-described belt driving system will be described referring to FIG. 15. As illustrated in FIG. 15, long timing belts 116, 117 extending in a sub-scanning direction are respectively arranged at both sides of a first moving carriage 104 in a main scanning direction. Further, short timing belts 118, 119 extending in the sub-scanning direction are respectively arranged at both sides of a second moving carriage 105 in a main scanning direction.
The timing belt 116 is spanned around a set of timing belt pulleys 120, 121, and the timing belt 117 is spanned around another set of timing belt pulleys 122, 123. Further, the timing belt 118 is spanned around a set of timing belt pulleys 124, 125, and the timing belt 119 is spanned around a set of timing belt pulleys 126, 127. The timing belt pulleys, 120 and 124, are intercoupled each other, and the timing belt pulleys, 122 and 126, are intercoupled each other. A drive shaft 128 connects the timing belt pulleys, 120 and 124, and the timing belt pulleys, 122 and 126. One end of the drive shaft 128 is connected to a driven pulley 129. The driven pulley 129 is connected to a drive pulley 132 of a drive motor 131 via a timing belt 130.
End portions 133 of the both sides of the first moving carriage 104 in the main scanning direction are respectively attached to the timing belts, 116 and 117. Further, end portions 134 of the both sides of the second moving carriage 105 in the main scanning direction are respectively attached to the timing belts, 118 and 119, such that the second moving carriage 105 is arranged parallel to the first moving carriage 104 spaced at a predetermined distance. The end portions 133 of the first moving carriage 104 and the end portions 134 of the second moving carriage 105 are moved in the sub-scanning direction along guide rails 113.
A driving force of the drive motor 131 is applied to the timing belt pulleys, 120, 122, 124, and 126, via the drive shaft 128, thereby rotating the timing belts, 116, 117, 118, and 119, and moving the first and second moving carriages 104, 105 in the sub-scanning direction. In this optical scanning device, each diameter of the timing belt pulleys, 124 and 126, is set to be one-half that of the timing belt pulleys, 120 and 122. Thereby, the first and second moving carriages 104, 105 move at a speed ratio of 2 to 1.
The assembly work of the above-described optical scanning device employing the belt driving system may be more easily accomplished than the optical scanning device employing the wire driving system. However, in the above-described background optical scanning device employing the belt driving system, from the theoretical point of view, the first and second moving carriages 104, 105 may not move at a speed ratio of 2 to 1, because the two types of the timing belts, 116, 117, and the timing belts, 118 and 119, undergo speed variations due to engagement errors and decentering of the timing belt pulleys. In this case, the distance between a lens and an original document is minutely changed, causing deterioration of scanned images.
Further, in the above-described background optical scanning device employing the belt driving system, a predetermined tension needs to be applied to each of the timing belts, 116, 117, 118, and 119, to convey the driving force of the drive motor 131 to the first and second moving carriages 104, 105. In the above-described construction of the background optical scanning device, the drive shaft 128 is subject to the tensions of the timing belts, 116, 117, 118, and 119, so that relatively large radial forces are exerted on bearings that rotatably hold the drive shaft 128, and radial forces are also exerted on the four driven timing belt pulleys, 120, 122, 124, and 126, resulting in a high drive load condition.
Moreover, in the above-described background optical scanning device employing the belt driving system, because the first and second moving carriages 104, 105 are coupled to the drive motor 131 via the timing belts, 116, 117, 118, and 119, when the operational condition of the drive motor 131 is switched, for example, between rotation and halt, forward rotation and reverse rotation, etc., the forces in the direction of hindering the movements of the timing belts, 116, 117, 118, and 119, are typically produced due to the inertial forces of the first and second moving carriages 104, 105. As a result, the attachment positions of the first and second moving carriages 104, 105 relative to the timing belts, 116, 117, 118, and 119, may be shifted, causing deformation of scanned images in the sub-scanning direction.
If the first and second moving carriages 104, 105 are attached to the timing belts, 116, 117, 118, and 119, at a plurality positions to avoid the above-described shifts of the attachment positions, assembly work inevitably may become complicated, thereby decreasing productivity.
According to one aspect of the present invention, an optical scanning device includes a housing, a first moving carriage carrying a light source provided to irradiate an image surface of an original document with light and a first mirror provided to reflect the light reflected from the image surface of the original document, a second moving carriage carrying at least one of a second mirror and a third mirror each provided to reflect the light reflected from the first mirror, the second moving carriage being configured to move in a sub-scanning direction at about one-half of a moving speed of the first moving carriage, a plurality of timing pulleys spaced apart in the sub-scanning direction and including at least a first timing pulley and a second timing pulley, a timing belt spanned around the first and second timing pulleys to reciprocate the first moving carriage in the sub-scanning direction, a drive device configured to drive the first timing pulley to rotate, a plurality of flat pulleys rotatably supported by the second moving carriage and spaced apart in the sub-scanning direction by a distance corresponding to a moving amount of the second moving carriage, a flat belt spanned around the plurality of flat pulleys to reciprocate the second moving carriage in the sub-scanning direction, an engaging member detachably engaging the timing belt and the flat belt to the first moving carriage, and a fixing member fixing the flat belt to the housing at a position different from a position where the flat belt is engaged to the first moving carriage by substantially half of a circumference of the flat belt. The plurality of timing pulleys, timing belt, plurality of flat pulleys, flat belt, engaging member, and fixing member are provided at each side of the first and second moving carriages in the main scanning direction.
According to another aspect of the present invention, an optical scanning device includes a moving carriage carrying an exposure optical system, a timing belt positioned along a sub-scanning direction to reciprocate the moving carriage in the sub-scanning direction, and a belt clamp mechanism detachably clamping the timing belt to the moving carriage, the belt clamp mechanism including, a plurality of comb-tooth members provided to a lower surface of the moving carriage spaced apart in the sub-scanning direction by a gap such that the plurality of comb-tooth members protrude from the lower surface of the moving carriage toward the timing belt, and a clamp member having a support surface having a protrusion protruding toward the gap between the plurality of comb-tooth members. The clamp member is secured to the moving carriage such that the clamp member opposes the plurality of comb-tooth members via the timing belt while the protrusion on the support surface pressing the timing belt into the gap between the pair of comb-tooth members.
Objects, features, and advantages of the present invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings.